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Parts or the Whole Content is From:
Printer and Photocopier Troubleshooting and Repair Collection
Version 2.48
Copyright © 1996-2001
Samuel M. Goldwasser
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How Laser Printer and Photocopier Works

Copiers and laser printers have a lot in common. The major difference is in how the image is formed on a photosensitive drum:

A copier uses a bright light and lens to focus an image of the original (actually, a strip at a time which is scanned in most modern low to medium performance copiers) onto the drum. Adjusting the lens-to-original and lens-to-drum distance is used to vary the reduction or magnification.
A laser printer uses a low power sharply focused laser beam to scan one line at a time on the drum. Modern laser printers use infra-red solid state laserdiodes similar to those used in CD players and optical disk drives while older ones used helium neon lasers.
The digital image is generated from a bit map stored in the printer's memory and modulates the laser beam. Scanning is mechanical - a high speed motor spins a multifaceted deflection mirror to get the X-axis and the paper moves to get the Y axis.
LED printers use a large array of LEDs as the image source but are otherwise similar to laser printers.
Plain paper fax machines use similar techniques in their printing mechanism.

Beyond this, copiers and laser printers are nearly identical (at least in principle) except that copiers use a positive process (dark areas in the original result in marks on the paper) and laser printers commonly use a negative process (a spot of light results in a dark mark on the paper).

The most sophisticated machines are now actually scanner-laser printer combinations with buffer memory so that multiple copies can be made without rescanning the original, sorting and collating is more flexible, scaling and rotation can be done digitally, and other features not possible with simple copiers.

The photosensitive drum is the heart of the laser printer or copier. In larger machines, it may be a separately replaceable unit. In most laser printers and smaller copiers, it is part of the 'toner cartridge' and is a throw-away (or may be recycled).

The drum is coated with a photosensitive material which has an extremely high resistance when in darkness. It's resistance drops to a low value when illuminated.

All of the following takes place as a continuous process as the drum rotates. Note that the actual photosensitive drum in most copiers and laser printers has a circumference that is much smaller than the length of the printed page. Therefore, only a portion fits at any given time and the charging, exposure, transfer to the paper, cleaning, and erasing is a continuous process:

The drum's surface is charged to a high positive voltage (typically 5 to 6 kV) by a set of charging corona wires in close proximity to the drum.

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The exposure process differs for copiers and laser printers:

For copiers, a swath of the original is focused onto the drum. As the drum turns, a quartz lamp and strip mirror moves along the original and second strip turning mirror moves at half this speed. The result is that the entire original's image is kind of 'peeled' onto the rotating drum. (Look through the glass platform that supports the original of a copier as it is copying and you will see what I mean.)
For laser printers, the negative image of the page stored in the printer's buffer memory (the laser is turned on where the print is to be black) is read out and scanned onto the drum one line (i.e., 1/300th or 1/600th of an inch) at a time.

Where the light hits the drum's surface, its resistance drops dramatically and the charge in these areas is dissipated.

At this point, a swath of the image of your ultimate copied or printed page resides as areas of electrostatic charge on the drum. This is a 'latent' image and must be 'developed'.

As the drum continues to turn, the latent image rotates past the 'developer unit' which contains a mixture of developer and toner. For the most part, developer is not really used up during the printing process but some is lost and may need to be replenished from time-to-time (depends on design).

Developer is a material which includes powdered iron or other powder which is attracted by a magnet.
Toner is the actual 'ink' and consists of very finely powdered thermo plastic particles. These are 'fixed' in the fuser by literally melting the image onto the paper.

Depending on design, the developer material may be separate or actually combined with the toner.

A magnet in the developer unit which is as long as the page is wide causes the developer along with trapped toner to stand out following its lines of force off of its long N-S pole pieces. This forms a kind of brush of toner and developer material which is in contact with the drum as it rotates with its latent image. Normally, the developer material brush is C-shaped, and toner particles are carried in the C-shape (the back of the 'C' is against the drum).

Here is where the developing processes of copiers and laser printers differ:

For copiers, the relative charges of the drum and toner are set up so that toner is drawn to the unexposed (dark parts of the original) portions of the drum resulting in a positive image on the paper.
For laser printers, the relative charges of the drum and toner are set up so that toner is drawn to the exposed (where the laser beam was turned on) portions of the drum resulting in a negative image on the paper.

The drum continues to rotate around and comes in contact with the paper.

Below the paper is another corona, the 'transfer corona'. Another high voltage is applied to the back of the paper (once again, around 7 or 8 kV DC) to draw the toner from the drum to the paper. (Remember, all this is going on in a continual cycle and it is all in motion).

Depending on the manufacturer of the machine, you may or may not have a third corona, the 'separation corona'. This is needed to separate the paper from the drum, but not disturb the toner on the paper (the separation corona is usually 4 or 5 kV AC (if it was DC, you would separate the paper, but have *very* smeared toner all over the page as to make it unreadable). The separation corona usually has guides over it to keep the paper from 'dipping' down too far into the corona shell.

Paper is then transported to the fuser which 'fixes' the toner to the paper via heat (to soften the toner particles) and pressure (to embed them in the paper fiber). There are parts in the fuser which also keep the paper from sticking to the hot rollers. A thermostatically controlled quartz tube lamp provides the heat inside the anti-stick (Teflon coated) fuser roller.

Finally, your copy or printed page is ready!

However, we are not done as there is still some toner on the drum - it is not possible to get it all off electrically) so there is usually a rubber or plastic blade which rubs in direct contact with the drum. This 'drum blade' scrapes the toner off the drum, and the 'recovery blade' catches it to keep it from falling back into the machine. A 'used toner auger' transports the used toner (which is now changed both physically and electrically and is also contaminated with paper dust (don't reuse your used toner) because it can eventually damage the developer unit, cleaning blades, fuser sections and other parts of the mechanism.

Now that all the toner has been scraped off the drum, there is still some residual charge on the drum from the previous exposure process. You can't scrape the static charge off the drum, so the cleaned drum is now fully exposed to a bright light to discharge the drum surface and prepare it again for a new charge, which comes right after the discharge lamps.

That is the basic process. Many variations are possible and depending upon the machine and manufacturer, some of this may be a little different. Where a (disposable) toner cartridge is used, many of these components are replaced with the cartridge - typically the drum, toner itself and developer (usually combined into a single powder), developer magnet (really neat!), cleaning blades, some of the corona wires.

Bannk.com the place for Cheap Printer Inkjet Cartridges Presents: 'How Laser Printer and Photocopier Works'

Bannk.com the place for Cheap Printer Inkjet Cartridges Presents:
'How Laser Printer and Photocopier Works'